Liquid ebony if it hasn't been suggested yet. 3M also makes a similar swirl remover.
Since I'm going to show N shines now I picked up the 18 volt 6" Ryobi orbital from their 1-Plus line of 18 volt tools...inexpensive ($29.95 at HD) and wonderful to use...like someone said you can only damage the paint if you drop it on the car, LOL! We wouldn't do that would we? For heavier work Ryobi also has a two speed 18 volt grinder ($39.99) which I outfitted with a foam buffing head...be careful though it can burn if you aren't careful.
Good luck, sounds like you have a years worth of vehicles to do!

Terry